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Some plants have evolved to increase their chances of survival by being drought-adapted. Among those plant species is Heteromeles arbutifolia, native to California. Logically, the fact that Heteromeles arbutifolia tolerates the low supply of water makes this plant more likely to be within environments where the level of sun exposure is high. Thus, we hypothesized that lowering soil moisture will cause an increase in xylem pressure, causing an increase in photo-protection and florescence, and a decrease in photosynthetic rate. This has not been tested before on a native chaparral plant such as Heteromeles arbutifolia. The experiment was held as following: six H. arbutifolia were evenly divided up into a treatment group and a control group. Both groups were given equal hydration at the beginning of this experiment. From then on the control group maintained a constant daily rate of hydration as the experimental groups received no water. Data of photosynthesis, photo-protection, florescence, xylem pressure, and soil moisture were taken for both groups throughout the entire experiment. Data collection showed statistically significant results of comparing non-photosynthetic quenching to photosynthetic quenching in water-stressed plants and water-saturated plants. Significant correlations were drawn between the following: the fraction of non-photosynthetic quenching to xylem pressure, the fraction of non-photosynthetic quenching to soil moisture, the fraction of non-photosynthetic quenching versus the time since the last event of irrigation, and xylem pressure and the time since the plant was last irrigated. It was concluded that photo-protection rate increases with water stress, which supported the initial hypothesis in part. However, the study also concluded that there was not a significant difference between the two groups regarding the florescence rate.

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